Since an acrylic rubber has excellent heat resistance and oil resistance, etc., it is widely used as a material of rubber parts to be used in a state of contacting oil, etc., such as seals, hoses, tubes and belts, etc. in the automobile-related fields, etc. An acrylic rubber is subjected to cross-linking to obtain rubber elasticity so as to be used as these rubber parts. For that purpose, it is copolymerized with a cross-linkable monomer having an active cross-linking point normally in an amount of 1 to 5 wt % or so. Such a cross-6 linkable acrylic rubber is demanded to have small permanent compression set as well as excellent heat resistance and cold resistance and, furthermore, there has been a demand for those also having excellent fuel oil resistance and excellent scorch stability.
Selection of the cross-linkable monomer to be copolymerized with an acrylic rubber as well as a cross-linking agent to be used in combination therewith results in determining a cross-linking reaction speed, so that it affects storage stability, mechanical characteristics, permanent compression set and heat resistance, etc. Generally, as a cross-linkable monomer to serve as such a cross-linking agent, 2-chloroethylvinyl ether, vinylchloro acetate and other chlorine based monomers, allylglycidyl ether and other epoxy based monomers may be used.
As cross-linkable monomers, maleic acid, fumaric acid and other butenedionic acid monoesters, specifically, butenedionic acid monobutyl ester has been also studied. Among them, a cross-linked product of an acrylic rubber composition formed by including an aromatic diamine cross-linking agent and a guanidine compound cross-lining auxiliary in an acrylic rubber obtained by copolymerizing with 0.1 to 10 wt % of monolower alkyl ester of fumaric acid has been reported to exhibit excellent heat resistance and cold resistance (the patent article 1). However, these acrylic rubber compositions were poor particularly in scorch stability.
Also, it has been reported that when using an acrylic rubber composition obtained by copolymerizing alkoxyalkyl acrylate, acrylonitrile in an amount of 10 to 15 wt % and a necessary amount of cross-linkable monomer as an automobile fuel hose, fuel impermeability can be improved while maintaining sour gasoline resistance and amine resistance, etc. (the patent article 2). However, the composition has a disadvantage that the cold resistance and heat resistance become poor.
Furthermore, it is reported that a composition obtained by blending a specific cross-linking agent and a specific amine compound in a carboxyl group containing acrylic rubber including a specific structure unit derived from methacrylonitrile does not adhere to metal surfaces and does not cause scorch at the time of processing and that an obtained cross-linked product has excellent heat resistance, cold resistance and degraded oil resistance (the patent article 3). However, the composition does not have enough cold resistance and fuel oil resistance.
The patent article 1: The Japanese Unexamined Patent Publication No. H11-92614
The patent article 2: The Japanese Unexamined Patent Publication No. 2001-146540
The patent article 3: The Japanese Unexamined Patent Publication No. 2003-342437